Hyuck Lim

Amorphous gallium indium zinc oxide thin film transistors: Sensitive to oxygen molecules

In this study, the authors report characteristic of indium gallium zinc oxides (GIZOs) which is strongly associated with the film surface. In ambient air, turn-on voltage of GIZO thin film transistors is approximately −7V. However, at the pressure of 8×10−6Torr, the turn-on voltage dramatically shifts to nearly −47V of the negative gate bias direction. When the oxygen is introduced in the chamber, the turn-on voltage returns to the normal value, that of air. It is believed that the adsorbed oxygen forms depletion layer below the surface, resulting in Von shifts. The carrier concentration of the channel varies from 1×1019to1×1020cm−3 due to oxygen adsorption.

Full Integration of Highly Manufacturable 512Mb PRAM based on 90nm Technology

Fully functional 512Mb PRAM with 0.047mum2 (5.8F2) cell size was successfully fabricated using 90nm diode technology in which the authors developed novel process schemes such as vertical diode as cell switch, self-aligned bottom electrode contact scheme, and line-type Ge2Sb2Te5. The 512Mb PRAM showed excellent electrical properties of sufficiently large on-current and stable phase transition behavior. The reliability of the 512Mb chip was also evaluated as a write-endurance over 1E5 cycles and a data retention time over 10 years at 85degC

Source/Drain Series-Resistance Effects in Amorphous Gallium–Indium Zinc-Oxide Thin Film Transistors

In this letter, we investigated the effects of source/drain series resistance on amorphous gallium-indium-doped zinc-oxide (a-GIZO) thin film transistors (TFTs). A linear least square fit of a plot of the reciprocal of channel resistance versus gate voltage yields a threshold voltage of 3.5 V and a field-effect mobility of about 13.5 cm2/Vldrs. Furthermore, in a-GIZO TFTs, most of the current flows in the distance range of 0-0.5 mum from the channel edge and shorter than that in a-Si:H TFTs. Moreover, unlike a-Si:H TFTs, a-GIZO TFTs did not show an intersection point, because they did not contain a highly doped ohmic (n+) layer below the source/drain electrodes.

Program/Erase Characteristics of Amorphous Gallium Indium Zinc Oxide Nonvolatile Memory

Currently, both high-density 3-D stacking nonvolatile (NV) memory and embedded NV memory in advanced systems on panel (SOPs) urgently demand the assistance of new and functional transition metal-oxide materials. This is to overcome serious fabrication issues encountered in the use of conventional Si or poly-crystalline Si materials, as well as to increase storage density with lower process cost. This paper reports the fully functional NV memory structure operated by an ionic amorphous oxide semiconductor with a wide energy band gap (> 3.0 eV) in a Ga2O3-In2O3-ZnO (GIZO) system under low process temperature (< 400degC) while being combined with various metal-oxide materials of Al2O3, GIZO, and Al2O3 as the electron charges tunneling, storage, and blocking layers, respectively. The different methods of memory programs and, especially, the unique erase characteristics caused by a much wider band gap than Si were intensively being investigated, and as a result, excellent electrical results of a large program/erase window over 3.8 V at a pulse time of 10 ms are achieved.

Double gate GaInZnO thin film transistors

We fabricated gallium-indium-zinc oxide (GIZO) thin film transistors (TFTs) having a double-gated (DG) structure and studied the back gate effect on device performance. DG GIZO TFTs showed better threshold voltage (Vth), swing factor (S), and on/off current than those with a single gate. With the variation in back gate bias, the device performance significantly changes due to the modification of field distribution near the GIZO channel. It is believed that our DG structure is an effective way to improve the performance of GIZO oxide transistors and suppress the formation of an accumulation layer at the back surface.

Highly Stable Ga2O3-In2O3-ZnO TFT for Active-Matrix Organic Light-Emitting Diode Display Application

We, for the first time, have successfully fabricated amorphous Ga ₂O₃-In₂O₃-ZnO thin film transistor (TFT) with excellent electrical properties and good stability under constant current stress. This transistor shows a field effect mobility of 10 cm²/Vs, an off current below 2 pA and a drain current on-to-off ratio of above 10⁸. The threshold voltage shift was less than 0.2 V for 100 hours at 3 muA and 60 degC. Such stable oxide transistors can be utilized as driving transistor for large area OLED display

Low-Temperature Process for Advanced Si Thin Film Transistor Technology

Low-temperature Si thin film transistor (TFT) and its possibility as a new device process are described. Currently, an extensive study is performed in order to realize an advanced system on glass (SoG) by incorporating additional functional devices or circuits. By reducing further the process temperature down to 200 °C or below and by improving the fabrication process as an ultra-low temperature polycrystalline Si (U-LTPS), not only liquid crystal display (LCD) but also organic light emitting diode (O-LED) flat panel display (FPD) driven by using polycrystalline Si (poly-Si) TFTs is expected to be mounted on a flexible plastic substrate. Although technical issues to be solved remain for the fabrication of channels, gate insulator etc., it is possible for the Si TFT to be developed into a smart system on plastic for unique applications as well as a functional Si system-on-insulator in a ubiquitous information technology (IT) era.

Electrically controlled hydrophobicity in a surface modified nanoporous carbon

Conventional surface treatments lead to constant surface morphologies and properties. Here we show that as the inner surfaces of a nanoporous carbon are modified by 16-mercaptohexadecanoic acid through a two-step grafting process, due to the flexibility of the surface chains, the end groups can be repelled by negative surface charges and attracted by positive surface charges. Thus, the surface wettability is controlled electrically. The effective solid-liquid interfacial tension in the nanopores is analyzed in a pressure induced infiltration experiment.

Advanced poly-Si TFT with fin-like channels by ELA

The advanced low-temperature polysilicon (poly-Si) thin-film transistor with three-dimensional channels of fin-like profile has been demonstrated using excimer laser annealing and unique undercut structure without any additional patterning process. This approach provides a very narrow fin-like channel in devices with high ratio of film thickness to the width as well as a high-quality poly-Si film in channels with better crystallinity for the effect of columnar-like grain growth following the shrinkage of silicon stripe after laser irradiation. Due to that and the stronger electrical stress on the channel by the multigate, the new device with a fin-like channel structure shows good characteristics of the highest mobility up to 395 cm/sup 2//V/spl middot/s, a subthreshold voltage slope below 400 mV/dec, and an ON-OFF current ratio higher than 10/sup 6/.

Effects of ion concentration on thermally-chargeable double-layer supercapacitors

The concept of thermally-chargeable supercapacitor was discussed and validated experimentally. As two double-layer supercapacitor-type devices were placed at different temperatures and connected, due to the thermal dependence of surface charge structures, the electrode potentials became different, and thermal energy could be harvested and stored as electric energy. The important effect of ion concentration was investigated. The results were quite different from the prediction of conventional surface theory, which should be attributed to the unique behaviors of the ions confined in the nanoporous electrodes.